As long as your car radio is also capable of picking up FM broadcasts, then the Tunecast wil work. XM radio is a satellite radio service that is typically added to a car system that also has an AM/FM radio in it as well, so I imagine the Tunecast will work just fine.

I was recently given a red IPod Nano 7th generation device. I need an FM transmitter/charger for my car which does not have a connection built it. The device would have to be plugged into my cigarette lighter and the IPod plugged into the transmitter/charger. I use it mostly for the music from my car radio.

I have a very inexpensive device that I purchased two weeks ago from Amazon.com. Unfortunately, it only plays the recorded music/musicians with the vocalists sounding as though they are singing from an echo chamber. Doesn't sync the music to one recording.
It also had a cassette attachment. Totally unusable. My cassette player has auto reverse so the tape plays for one minute and reverses.

Yes owned it for a couple of years and just bought the iPhone 5. With the lighting to 30 pin adapter it works great. Make sure you buy the Apple white one. I bought a second adapter with a cord black knock off and it charged but you couldn't hear music had to send it back and buy a second white one. One for car and one for home.